The present invention claims the benefit of the Korean Patent Application No. 2001-89298 filed in Korea on Dec. 31, 2001, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to an organic electro luminescence device, and more particularly, an organic electro luminescence device with low-resistance wiring.
2. Description of the Background Art
An organic electro luminescence display using an electro-luminescence (EL) device is seen as the next generation display device after the cathode ray tube (CRT) and a liquid crystal display (LCD). Its applicability is wide spread and an EL device is used as a display in devices such as portable terminals, car navigation systems (CNS), game machines, notebook computers, and wall-type televisions. Generally, an organic electro luminescence display includes a matrix of electro luminescence devices each including an organic emitting layer positioned between a positive electrode and a negative electrode. Light is emitted from the organic emitting layer when a voltage is applied across the positive electrode and the negative electrode.
More specifically, the positive electrode is formed by sputtering indium-tin-oxide (ITO) on a glass substrate having switching and drive circuits and then patterning the ITO such that the electrode is connected to a drive circuit. An organic emitting layer including a hole transport layer, an emitting layer, and an electron transport layer are then formed on the ITO film. A negative electrode is then formed on the organic emitting layer. The negative electrode is a metal having low work function so as to readily supply electrons to the organic emitting layer. The ITO of the positive electrode has a high electrical conductivity so that holes can be readily supplied to the organic emitting layer. Further, the ITO has high light transmittance so that light emitted from the organic emitting layer can be transmitted through the positive electrode. Thus, when positive and negative voltages are applied to the positive electrode and to the negative electrode, respectively, the holes injected from the positive electrode and the electrons injected from the negative electrode cause the organic emitting layer to emit light.
In an organic electro luminescence display, unit pixels each containing an organic emitting layer are disposed in a matrix form. The organic emitting layers of the unit pixels are selectively driven through thin film transistors disposed in each of the respective unit pixels to display an image. The organic electro luminescence display described above will be described in more detail with reference to accompanying FIG. 1 showing an equivalent circuit for configuring and operating the thin film transistors in accordance with a voltage driving method.
As shown in FIG. 1, each unit pixel includes a first thin film transistor 10 and a second thin film transistors 20, and an organic luminescence device 30. The unit pixel is defined by a gate line Gn for supplying a gate signal to the gate of the first thin film transistor 10 in a row direction, a data line Dm for supplying a data signal to the source of the first thin film transistor 10 in a column direction, a power line Pm for supplying electric power to the source of the second thin film transistor 20 in a column direction and a gate line of another pixel area in a row direction. The first thin film transistor 10 includes a gate electrode 11 connected to the gate line Gn to be supplied with the gate signal, a source electrode 12 connected to the data line Dm to be supplied with the data signal, and a drain electrode 13 connected to a gate electrode 21 of the second thin film transistor 20. The second thin film transistor 20 includes the gate electrode 21 connected to the drain electrode 13 of the first thin film transistor 10, a drain electrode 22 connected to a pixel electrode, and a source electrode 23 connected to the power line Pm. The organic luminescence device 30 includes an organic emitting layer 31 positioned between a cathode electrode (not shown) and an anode electrode (not shown), wherein the organic emitting layer 31 includes a hole transport layer (not shown), an emitting layer (not shown), and an electron transport layer (not shown). In addition, a capacitor 40 is included in which one electrode is connected to the power line Pm and the other electrode is connected both to the drain electrode 13 of the first thin film transistor 10 and to the gate electrode 21 of the second thin film transistor 20.
Hereinafter, the operation of the equivalent circuit for the unit pixel of the organic electro luminescence display device shown in FIG. 1 will be described in detail as follows. When the gate signal is applied to the gate electrode 12 from the gate line Gn, the first thin film transistor 10 is turned on, and therefore, the data signal supplied from the data line Dm is supplied to the gate electrode 21 of the second thin film transistor 20 through the source electrode 12 and the drain electrode 13 of the first thin film transistor 10. Thus, the potential of the gate electrode 21 becomes the same as that of the data line Dm.
The degree of turn on for the second thin film transistor 20 is decided by the potential supplied to the gate electrode 21, and therefore, electric current corresponding to the potential supplied to the gate electrode 21 is supplied to the organic luminescence device 30 from the power line Pm. The organic luminescence device 30 emits light according to the amount of electric current supplied. Thus, the brightness of the light emitted from the organic luminescence device 30 is determined by the value or voltage of the data signal, which is applied through the data line Dm.
Generally, in a display device having a matrix form, a gate signal is supplied to the first gate line and then to the rest of the gate lines sequentially such that an image is displayed on the screen after the sequence is completed across the display. The capacitor 40 in a unit pixel stays charged to the potential of the data signal to maintain the luminescence of the organic luminescence device 30 in the unit pixel until another data signal is supplied corresponding to another gate signal from the gate line Gn of the unit pixel. Thus, the amount of light from each unit pixel can be changed each time a gate signal is sequentially applied across the display to all of the gate lines Gn.
FIG. 2 depicts an equivalent circuit diagram of an organic electro luminescence device for configuring and operating the thin film transistors according to a current driving method. As shown in FIG. 2, a unit pixel includes a first thin film transistor 210 and a second thin film transistors 220 for switching, a third thin film transistor 230 and a fourth thin film transistor 240 for driving, and an organic luminescence device 250. The area of the unit pixel is divided by gate line Gn for supplying a gate signal to the unit pixel, and is in between the data line Dm for supplying the data signal to the unit pixel and the power line Pm for supplying electric power to the source of the fourth transistor 240 of the unit pixel.
When a gate signal is supplied from the gate line Gn, the first switching thin film transistor 210 is turned on, and therefore, the data signal supplied from the data line Dm is supplied to the source electrode 232 and to the gate electrode 231 of the third thin film transistor 230 through the source electrode 212 and drain electrode 213 of the first thin film transistor 210. At the same time, the gate signal is also applied to the gate electrode 221 of the second thin film transistor 220 from the gate scan line Gn such that the second thin film transistor 220 is also turned on. The amount of current flowing through the drain electrode 233 and the source electrode 232 of the third thin film transistor 230 from the power line Pm is determined by the data signal supplied to the source electrode 232 and to the gate electrode 231 of the third thin film transistor 230. In addition, the same amount of current is supplied to the organic luminescence device 250 through the source electrode 242 and the drain electrode 243 of the fourth thin film transistor 240 from the power line Pm. Therefore, the third thin film transistor 230 and fourth thin film transistor 240 operate as current mirrors in driving the organic luminescence device 250. The brightness or intensity of the light emitted from the organic luminescence device 250 is proportionate to the amount of current supplied to the organic luminescence device, and the amount of current supplied to the organic luminescence device 250 is determined by the value or voltage of the data signal supplied from the data line Dm. Thus, the brightness or intensity of the light is determined by the data signal supplied from the data line Dm during the application of a gate signal from the gate line Gn.
However, in the organic electro luminescence displays as described above, the length of the gate line, data line, and the power line plays a role in displaying an image uniformly in terms of the images brightness arcross the display. The resistance along a gate line, data line and power line has more effect on the image uniformity in larger displays, since these lines are longer in larger displays. For example, the difference in brightness in a large organic electro luminescence display increases along a direction parallel with the gate line in the case of each pixel having 2-TFTs to drive an organic electro luminescence device with voltage. In another example, the difference in brightness in a large organic electro luminescence display increases in a direction parallel with the data line in the case of each pixel having 4-TFTs to drive an organic electro luminescence device with current.
Therefore, copper (Cu), that is, metal of low resistance is used as the wires in order to minimize the resistance of the gate line, data line, and power line. However, copper has low adhesion to insulating layers. Further, copper tends to diffuse into insulating layers, which significantly degrades the dielectric properties of the insulating layers.
Accordingly, the present invention is directed to an organic electro luminescence device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an organic electro luminescence device which is able to improve image quality of a display by minimizing the resistance of the gate line, and/or both the data line and the power line without degrading the dielectric properties of the insulating layers or the adhesion of the lines to the insulating layers.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an organic electro luminescence device including a gate line for supplying a gate signal, a data line for supplying image information that crosses the gate line, a pixel area adjacent to where the gate line and the data line cross each other, an organic emitting layer formed in the pixel area, a switching unit for switching image information supplied from the data line in response to the gate signal supplied from the gate line, a driving unit for applying an electric field across the organic emitting layer according to the image information supplied through the switching unit and a power line for providing the driving unit with a source voltage, wherein at least one of the gate line, data line and power line is a three-layer structure having an intermediate layer made of copper.
In another aspect, the an organic electro luminescence device includes a gate line for supplying a gate signal, a data line for supplying image information that crosses the gate line, a pixel area adjacent to where the gate line and the data line cross each other, an organic emitting layer formed in the pixel area, a switching unit for switching image information supplied from the data line in response to a gate signal supplied from the gate line, a driving unit for applying electric field across the organic emitting layer according to the image information applied through the switching unit and a power line, which is a first three-layer structure including an intermediate layer made of copper, for providing the driving unit with source voltage.